Add junitSelectors instrumentation argument for batched method and invocation selection - #416

Problem

The class instrumentation argument is read by two components at once: AndroidX's TestRequestBuilder and this runner's ParsedSelectors. AndroidX applies its method filter to the reported test names, which for JUnit Jupiter are display names (display named failing, param(int) - [2] 2). So:

• Selecting more than one method of the same class in a single run, e.g. -e class 'com.Foo#a,com.Foo#b', filters out the whole class, and 0 tests run. This holds whenever a selected method's display name differs from its Java name, including parameterized and repeated tests.
• A single invocation of a parameterized or repeated test cannot be selected at all.
• Running one method at a time works, because the runner switches to the legacy name format, but it costs one am instrument start-up per method.

This matters for tools that re-run failed tests: they want one instrumentation run for all failures, with names that match the original run.

Change

A new instrumentation argument, junitSelectors, read only by this runner:

-e junitSelectors "com.Foo#method,com.Foo#param[2],com.Foo$Inner#test,com.Bar"

• com.Foo#method selects a method (all overloads with that name)
• com.Foo#method[n] selects the n-th invocation (1-based, as in the display name) of a @TestTemplate method such as @ParameterizedTest or @RepeatedTest; for other methods the index is ignored
• com.Foo selects the class
• com.Foo$Inner#test selects methods of @Nested classes through their enclosing class. AndroidX's class scan does not hand nested classes to the runner on its own
• Classes that are not mentioned run nothing
• When this argument is present it takes precedence over class, and the normal (non-legacy) name format is kept, so reported names match a full run

The argument is parsed once in JUnitFrameworkRunnerParams.create(), like configurationParameters, environmentVariables and systemProperties.

Tests

• New JUnitSelectorsTests (12 cases): several methods of one class, single invocations of parameterized, repeated and nested parameterized tests, nested methods and classes, dynamic tests through their factory, unknown classes, whitespace and duplicates
• testFiveDebugUnitTest and testSixDebugUnitTest: 109/109 pass
• Checked on an Android 15 (API 35) emulator with JUnit 6.1.3. One run with 11 selectors across 5 classes, including two @Nested classes and param[2], executed exactly the selected tests, and only invocation 2 of the parameterized test. Reported names matched a full run in both the instrumentation output and logcat.

The new tests are written with JUnit Jupiter, not added to AndroidJUnitFrameworkTests, because that JUnit 4/Robolectric class is not picked up by the current unit test tasks (no vintage engine).

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